Lb. Nguyen et al., REINNERVATION OF STRATUM LUCIDUM BY HIPPOCAMPAL MOSSY FIBERS IS DEVELOPMENTALLY-REGULATED, Developmental brain research, 95(2), 1996, pp. 184-193
Messy fibers from dentate gyrus granule cells establish synapses on CA
3 pyramidal neurons during the first 3 postnatal weeks in the rat. Mes
sy fiber synapses are primarily restricted to the stratum lucidum. Whe
n examined by Timm stain after 10-14 days in vitro, cultured hippocamp
al slices from postnatal 4 rat pups show a similar messy fiber termina
tion pattern in stratum lucidum. Thus, axon guidance cues used by mess
y fibers in vivo appear to be preserved in these cultured slices. Thre
e experimental manipulations were performed on hippocampal slice cultu
res to examine whether the axon guidance cues used by messy fibers;ire
developmentally regulated. First, massy fibers were transected on the
day of culture or day 7 in vitro. Messy fibers transected on either d
ay were able to reestablish their synaptic pattern in stratum lucidum
of CA3, Second, dentates and hippocampi of same age or different age w
ere co-cultured. Same age co-cultures P4 dentates to P4 hippocampi or
P11 dentates to P11 hippocampi) showed good messy fiber reinnervation
of stratum lucidum, as did different age co-cultures from P4 dentates
to P11 hippocampi. However, P11 dentates to P4 hippocampi co-cultures
showed little messy fiber reinnervation of stratum lucidum. Third, new
P4 or P11 dentates were co-cultured onto hippocampal slices in which
messy fibers had been allowed to degenerate, New messy fibers reinnerv
ated these hippocampi, but did not reestablish their normal synaptic p
attern in stratum lucidum. These three experimental manipulations sugg
est that messy fiber axon guidance mechanisms are developmentally regu
lated, and that existing messy fibers play a role in directing messy f
iber reinnervation of stratum lucidum.